X-Band radar improves rainfall, creek flow predictions

How rainfall will affect creek flows is an important piece of information when you’re trying to keep the public informed about potential flood risks. To figure it out, it helps to know exactly where the rain is falling, and to predict where it will fall with greater accuracy.

So Valley Water is getting a little help doing just that with a device called the X-band radar. Sitting atop our Penitencia Water Treatment Plant in the county’s east foothills, the X-band radar is part of a larger collaboration between Sonoma County Water, Colorado State University, the Department of Water Resources, National Oceanic and Atmospheric Administration, and many other agencies to deploy four X-band radars and one C-band radar around the Bay Area. The network of radars will work together, with the C-band radar looking off the coast to predict what is coming, and the X-band radars providing full radar coverage of the Bay Area, as well as detailed measurements of real time precipitation.

Valley Water participated in a pilot project, with an X-band radar atop Penitencia Water Treatment Plant, in 2016 during Super Bowl 50. The radar collected data and sent it to Colorado State University for processing. It was then returned to NOAA and us. The results provided proof of concept, so the same device was reinstalled in September 2017, with plans for a brand new replacement unit for long-term use to be installed this spring.

This new network of radars will both fill in gaps in existing radar coverage and improve accuracy of real-time precipitation data, collecting data every 1-2 minutes at a resolution of about 100 meters. That’s compared with existing S-band radars that collect data approximately every 6 minutes at 1 kilometer resolution. The data will be used to create “nowcasts” which are a look at the next 30-60 minutes. It will also initialize NOAA’s High-Resolution Rapid Refresh near-term forecast model every hour. Basically, the improved data will give us a better idea of what exactly is coming in the next few days. We can use that information in creek flow forecasting to determine how much water will flow down creeks and how high their levels could get with the predicted rainfall.

This winter, the X-band radar has been collecting valuable data of the several atmospheric rivers that have hit the area, and the radar data has been posted to a website for download by Valley Water. After all the radars are installed, it will be used for improving local NOAA forecasts, which will in turn, improve our forecasting of creek flows. We are committed to doing what we can to make the prediction of creek flows more accurate.

The X-band radar’s higher-resolution image of rains on Feb. 14, 2019, is on the left, and the Doppler image is on the right.

Here, the X-band radar image of rain on March 6 is on the right and the Doppler image is on the left.